1. Technical Field
The present disclosure relates to a socket and a semiconductor device including the socket and a semiconductor package connected to the socket.
2. Related Art
Various techniques have been disclosed for sockets that are used for electrical connection between electronic components.
For example, a structure is known in which connection pads of an LGA (land grid array) semiconductor package are brought into pressure contact with contacts of a high-springiness socket in connecting the semiconductor package to a mounting circuit board via the socket (see e.g., U.S. Pat. No. 7,264,486).
However, in the structure for connecting an LGA semiconductor package to a mounting circuit board using a socket as disclosed in U.S. Pat. No. 7,264,486, for example, the thickness of the socket is generally larger than 4 mm. Furthermore, this structure is associated with a problem that it cannot be used for products that are strongly required to be reduced in thickness and weight because the structure needs a heavy reinforcement member such as a back plate.
A structure for connecting a semiconductor package to a mounting circuit board using a socket will be described below with reference to a semiconductor device 101 shown in FIG. 8, which uses a socket as disclosed in U.S. Pat. No. 7,264,486.
As shown in FIG. 8, the semiconductor device 101 has a structure that an LGA semiconductor package 103 in which a semiconductor chip 105 is mounted on its top surface and its bottom surface is formed with electrical conduction terminals (hereinafter referred to as pads) 131 is connected to a mother board 104 (mounting circuit board) via a socket 102.
In this connection structure, in the socket 102, metal contacts 121 are inserted in through-holes 129 of a housing 120, which are located at such positions as to face the respective pads of the LGA semiconductor package 103. The housing 120 is made of an insulative resin. Tip portions 121a of the contacts 121 are in contact with the respective pads 131 of the semiconductor package 103. On the other hand, rear end portions (base portions) 121b of the contacts 121 are fixed (joined) to the mounting circuit board 104 with solder balls 160.
To ensure the electrical connections, the LGA semiconductor package 103 is fixed to the socket 102 in a state that the former is pressed, by strong force, against (and into) the latter in the direction (indicated by arrows in FIG. 8) that is perpendicular to a pad formation surface 130a. The force is applied to the top surface of a heat spreader 109 which is provided on the semiconductor package 103.
For example, the semiconductor package 103 has outer dimensions of about 35 mm×35 mm or about 45 mm×45 mm and is provided with about 1,400 pads 131. Therefore, the socket 102 which is connected to the semiconductor package 103 is also provided with about 1400 contacts 121. Therefore, to bring each contact 121 into contact with the corresponding pad 131 with prescribed pressure, the semiconductor package 103 needs to be pressed against the socket 102 by strong force of about 20 to 30 kgf.
In the semiconductor device 101, the prescribed pressure that is necessary for the connection is obtained by pressing the semiconductor package 103 against the socket 102 by means of a pressing means (urging member) 106. However, the strong force that is applied to the socket 102 in the direction perpendicular to the pad formation surface 130a acts on the mounting circuit board 104 as it is. Therefore, to prevent a warp or breakage of the mounting circuit board 104, the bottom surface of the mounting circuit board 104 is provided with a back plate 108 which serves as a reinforcement member for receiving the force. The back plate 108 is fixed, via support members 151, to a frame body 107 in which the pressing means (urging member) 106 is provided. For example, the back plate 108 is made of an iron-based material, and is a heavy component that weighs up to 150 g.
In semiconductor devices in which a semiconductor package is connected to a mounting circuit board via a socket as described above, recent increase in the number of pins of a semiconductor chip requires reduction in the socket-side terminal pitch. However, in the above-described semiconductor device 101, it is difficult to reduce the socket-side terminal pitch while giving each contact 121 a sufficient operation area for good electrical contact because of restrictions relating to the design of the contacts 121 and insufficient strength of the housing 120.
In addition, to secure good electrical contact, strong force needs to be applied to the socket 102 in the direction perpendicular to the pad formation surface 130a. This necessitates a component (e.g., back plate 108) that is heavy and makes the structure complex. Such a component is an obstruction to reduction in thickness and weight of an electrical product incorporating the semiconductor device 101.
Furthermore, to increase the processing speed of the semiconductor device 101, the socket 102 is required to be reduced in thickness. However, it is difficult to satisfy this requirement because of the same reasons mentioned above, that is, restrictions relating to the design of the contacts 121 and insufficient strength of the housing 120.